JPH09178578A - Capacitive sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitive sensor which can be reduced in size while preventing intrusion of dust into a sensor gap. SOLUTION: The capacitive sensor comprises a fixing board 10 and a semiconductor substrate 20 subjected to anodic joint. The semiconductor substrate 20 is provided with a sensor gas, i.e., a recess 22, at a part where a diaphragm 21 is formed. A wiring trough 23 is made between the recess 22 and a step part 24. The wiring trough 23 extends in parallel with the step part 24 and bent, in the way, toward the step part 24. A first insulation film 26 is formed over the step part 24 and wiring trough 23 and a second insulation film 27 is formed thereon. A constricted part 28 is formed in the wiring trough 23 by the second insulation film 27. A third insulation film 30 is formed on the part 29 of semiconductor substrate 20 exposed to the step part 24 side. A connection electrode 12 extending from a fixed electrode 11 and a connection electrode 32 extending from a wire bonding pad 31 are pressed in the wiring trough 23.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a capacitance-type sensor that detects pressure, vibration, acceleration, and other physical quantities based on capacitance.

[0002]

BACKGROUND ART Capacitive sensors include pressure sensors that detect the pressure of fluid such as air and liquid, and acceleration sensors that detect acceleration, vibration, and the like.

FIG. 10 is a partially cutaway plan view showing a conventional electrostatic capacity type semiconductor pressure sensor, and FIG. 11 is XI-XI of FIG.
12 is a sectional view taken along line XII-XII in FIG. In FIG. 11 and FIG. 12, the wall thickness (particularly the wall thickness of the electrode and the insulating film) is drawn thicker than the actual thickness for convenience of drawing and easy understanding.

The capacitance type pressure sensor is constructed by anodic bonding a silicon semiconductor substrate 101 and a fixed substrate 102 made of an insulating material such as glass.

On the silicon semiconductor substrate 101, a thin diaphragm 103 is formed by scraping off the lower surface (in FIGS. 11 and 12) by etching. The upper surface of the semiconductor substrate 101 has a diaphragm 10
A circular recess 106 is formed at a position corresponding to 3.
Further, the step portion 10 for arranging the wire bonding pads 110 and 113 is provided on the right end portion of the upper surface of the semiconductor substrate 101.
4 is formed. Furthermore, on the upper surface of the semiconductor substrate 101, a linear wiring groove 10 that leads from the recess 106 to the step 104
7 is formed. Since the silicon semiconductor substrate 101 has conductivity, the diaphragm 103 acts as a movable electrode.

On the other hand, on the surface of the fixed substrate 102 facing the diaphragm (movable electrode) 103 (the lower surface of the fixed substrate 102),
The fixed electrode 105 is formed by vapor-depositing aluminum or the like. An elongated connecting electrode 108 extends outward from a part of the fixed electrode 105. The connection electrode 108 is formed on the lower surface of the fixed substrate 102 at a position corresponding to the wiring groove 107.

An insulating film is formed on the upper surface of the step portion 104 of the semiconductor substrate 101.
109 is formed, and the fixed electrode wire bonding pad 110 is formed on the insulating film 109. An elongated connecting electrode 111 extends from a part of the fixed electrode wire bonding pad 110 through the wiring groove 107 toward the recess 106. The connection electrodes 108 and 111 are formed to have a width slightly smaller than that of the wiring groove 107 so as not to contact the side surface of the wiring groove 107.

When the silicon semiconductor substrate 101 and the fixed substrate 102 are anodically bonded, the tip portion of the connection electrode 108 and the tip portion of the connection electrode 111 (these tip portions are called interconnecting pads) are used for wiring. It is crimped in the groove 107. As a result, the fixed electrode 105 and the fixed electrode wire bonding pad 110 are electrically connected.

After the semiconductor substrate 101 and the fixed substrate 102 are anodically bonded, the right end portion (shown by a chain line 102a) of the fixed substrate 102 is cut by dicing.

A hole 112 communicating with the silicon semiconductor substrate 101 is formed in the insulating film 109, and a wire bonding pad 113 for a movable electrode is formed in the hole 112. Fixed electrode 10
5 and movable electrode 103 are wire bonding pads 11
Wires bonded on 0 and 113 (not shown)
And an external capacitance measuring circuit (pressure detecting circuit; not shown).

The recess 106 formed in the semiconductor substrate 101 forms a pressure detecting gap (sensor gap), and the fixed electrode 105 and the movable electrode 103 face each other with this gap interposed. The atmosphere is introduced into the recess 106 through the wiring groove 107.

The pressure to be measured is applied to the diaphragm 103. The diaphragm (movable electrode) 103 is vertically displaced (vibrated) according to the measured pressure applied. A change in the gap between the movable electrode 103 and the fixed electrode 105 changes the capacitance C between the electrodes 103 and 105. This change in capacitance C or the reciprocal of capacitance C 1 /
A change in C (generally the inverse 1 / C is used as the sensor output) is converted into a signal representing pressure in the capacitance measuring circuit.

The conventional capacitance type pressure sensor having such a structure has the following problems.

(1) Dividing the wafer into a plurality of pressure sensor chips by dicing, or a part of the fixed substrate 102
When the 102a is cut off by dicing and when the pressure sensor is used, dicing dust and dust enter the sensor gap 106 from the wiring groove 107, and the diaphragm 10
Since the displacement of 3 is impeded, the sensor characteristics deteriorate.

(2) Since the etching step for forming the concave portion 106 and the etching step for forming the step portion 104 are performed separately, a double-etched region is generated due to a mask patterning shift or the like. Occasionally (step 114 in wiring trench 107). Such a step 114
When the semiconductor substrate 101 and the fixed substrate 102 are anodically bonded, an electric field concentrates on the corners of the stepped portion 114, and due to this, a part of the fixed electrode 105 is destroyed and the connection electrode 108 is discharged.
, 111 may be disconnected, or a protrusion may be formed on the surface of the silicon semiconductor substrate 101.

(3) Since a part of the silicon semiconductor substrate 101 is exposed at a portion (indicated by reference numeral 115) other than the bonding surface with the fixed substrate 102, a portion between the exposed portion and the wire bonding pad 110 is formed. Leak current flows, which causes capacity instability especially in high humidity conditions.

(4) The connection electrode 108 is provided between the sensor electrode (particularly the fixed electrode 105) and the wire bonding pad 110.
, 111 extend in a straight line, which increases the size of the sensor chip.

[0018]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a capacitance type sensor having a structure in which dust is unlikely to enter the sensor gap.

Another object of the present invention is to provide a structure capable of miniaturizing the capacitance type sensor.

A further object of the present invention is to prevent the generation of leak current flowing on the exposed surface of the semiconductor substrate.

Furthermore, the present invention is intended to prevent electrode breakage, disconnection, etc. when the semiconductor substrate and the fixed electrode are anodically bonded.

In the capacitance type sensor according to the present invention, the semiconductor substrate and the fixed substrate are bonded to each other, a detection gap is formed between the semiconductor substrate and the fixed substrate, and the semiconductor is placed in the detection gap. A part of the substrate serves as a movable electrode, the fixed electrode is formed on the fixed substrate at a position facing the movable electrode, and a fixed electrode pad is formed on one of the semiconductor substrate and the fixed substrate. On at least one of the substrate and the fixed substrate, a wiring groove is formed from the detection gap toward the fixed electrode pad, and a gap is formed between the wiring groove and the groove wall. A connection electrode for connecting the fixed electrode to the fixed electrode pad is provided.

This capacitance type sensor is used as a pressure sensor, an acceleration (vibration) sensor, or the like. In the case of a pressure sensor, a diaphragm that is deformed by the applied pressure is formed on the semiconductor substrate in the detection gap portion. In the case of an acceleration sensor, the semiconductor substrate may be provided with a weight that is displaced in the detection gap portion in response to an applied acceleration or vibration.

The fixed substrate may be an insulating substrate such as glass or a semiconductor substrate. When the fixed substrate is a semiconductor substrate, a part of the semiconductor substrate will serve as the fixed electrode.

The first feature of the present invention is that a constriction structure is formed in a part of the wiring groove.

The narrowed structure is formed, for example, by providing an insulating film on the inner surface of the wiring groove.

Since a part of the wiring groove in which the connection electrode is provided has a narrow structure, dicing dust or dust is detected from the wiring groove during the dicing process or when the sensor is used (sensor gap). It can prevent you from getting inside.

A second feature of the present invention is that the wiring groove is smoothly bent substantially at a right angle.

Instead of forming the wiring groove linearly toward the fixed electrode pad, the wiring groove can be extended laterally from the detection gap and bent substantially at a right angle to face the fixed electrode pad. Therefore, the wiring groove can be provided by utilizing the unnecessary space on the substrate, and the length thereof can be increased to the required extent. This enables the sensor to be downsized. Further, in particular, as described below, when the connection electrode is formed by crimping two electrodes, it is possible to secure a sufficient length for disposing and crimping these electrodes.

In one embodiment of the present invention, the connection electrode has a first connection electrode extending from a part of the fixed electrode through the wiring groove toward the wire bonding pad, and the wire bonding. A second connection electrode extending from the pad through the wiring groove toward the fixed electrode, wherein the first connection electrode and the second connection electrode are pressure-bonded in the wiring groove. There is.

A third feature of the present invention is that the wiring groove is formed in the semiconductor substrate and an insulating film is formed on the bottom surface of the wiring groove. This feature is particularly effective when the wiring groove has at least two portions having different depths, and the insulating film makes it possible to smoothly connect the boundaries of the portions having different depths.

When the semiconductor substrate and the fixed substrate are anodically bonded, it is possible to prevent the electric field from being concentrated on each part of the wiring groove. Therefore, it is possible to prevent the occurrence of protrusions on the surface of the semiconductor substrate, electrode breakage, and disconnection of the connection electrode due to the concentration and discharge of the electric field.

A fourth feature of the present invention is that the surface of the portion exposed to the outside on the side of the semiconductor substrate which is joined to the fixed electrode is covered with an insulating film.

This feature is particularly characterized in that the semiconductor substrate has a portion projecting from the joint portion with the fixed substrate, and this projecting portion is a step portion formed thinner than the joint portion with the fixed substrate. This is effective when the desired cut surface of the semiconductor substrate is exposed, and an insulating film is formed on this exposed cut surface.

Since the insulating film is formed on the exposed portion of the semiconductor substrate, it is possible to prevent the generation of leak current between the semiconductor substrate and the fixed electrode pad.
Sensor malfunctions are reduced.

[0036]

EXAMPLE FIG. 1 is an exploded perspective view of a capacitance type pressure sensor,
FIG. 2 is an enlarged plan view of a part of which is cut away, and FIG.
4 is a sectional view taken along line IV-IV of FIG. 2, and FIG. 5 is a sectional view taken along line VV of FIG. 6 to 9 are enlarged perspective views showing a process of forming an insulating film on a silicon semiconductor substrate. FIG. 6 shows a state in which the silicon semiconductor substrate is etched, and FIG. 7 shows a first insulating film on the silicon semiconductor substrate. FIG. 8 shows a state in which the second insulating film is formed, and FIG. 9 shows a state in which the third insulating film is formed. In these figures, the thickness direction is shown greatly enlarged for clarity.

The capacitance type pressure sensor is constructed by anodic bonding a fixed substrate 10 formed of an insulating material such as glass and a conductive silicon semiconductor substrate 20 (as described later). , The third insulating film 30 formed on the silicon semiconductor substrate 20 is slightly formed on the joint surface of the silicon semiconductor substrate 20 with the fixed substrate 10, but affects the anodic bonding of both substrates 10 and 20. It is not wide and thick enough to give).

A circular diaphragm (thin portion) 21 is formed on the semiconductor substrate 20 by cutting a part of the lower surface of the silicon semiconductor substrate 20 into a truncated cone shape. The diaphragm 21 may have other shapes, such as a rectangle. The diaphragm 21 having elasticity is displaced (vibrated) in the vertical direction when receiving the measured pressure from the lower surface thereof. Since the diaphragm 21 is made of silicon, it has conductivity and functions as a movable electrode.

A recess 22 for forming a detection gap (sensor gap) between the fixed electrode 11 and the diaphragm 21, which will be described later, is provided above the portion of the silicon semiconductor substrate 20 where the diaphragm 21 is formed. Has been formed. Also,
Wire bonding on the edge of the silicon semiconductor substrate 20
A step portion 24 for forming the pads 31 and 35 is formed.

Further, the silicon semiconductor substrate 20 is formed with a wiring groove 23 that connects the concave portion 22 and the step portion 24. The wiring groove 23 extends from a part of the recess 22 in parallel with the step portion 24, bends gently in the vertical direction so as to draw an arc in the middle, and
I'm heading to 24.

By forming the wiring groove 23 in the dead space on the side of the diaphragm 21, the recess 22 and the step portion 24 are formed.
Since the gap L (see FIG. 2) between and can be narrowed, the sensor can be downsized. Further, the bent portion of the wiring groove 23 is not bent at a right angle, but is bent so as to draw a gentle arc shape, and the connection electrodes 12 and 32 to be described later are provided along the wiring groove 23. When the substrate 10 and the silicon semiconductor substrate 20 are anodically bonded, the electric field does not excessively concentrate on the bent portion.

The recess 22 may be formed on the surface of the fixed substrate 10 facing the diaphragm 21. In this case, the wiring groove 23 will also be formed in the fixed substrate 10.

The recess 22 and the stepped portion 24 are preferably formed in two steps by wet etching using an alkaline etching solution or dry etching using gas plasma or the like.

Referring to FIG. 6, the step 24 and the half region 23a of the wiring groove 23 on the step 24 side are deeply removed from the upper surface of the silicon semiconductor substrate 20 by the first etching process. Next, by the second etching process, the recess 22 and the half region 23b of the wiring groove 23 on the recess 22 side are shaved off. In the wiring groove 23, a region (step 2
5) can be formed.

Further, by the third wet etching process using the potassium hydroxide solution, the portion corresponding to the back side of the recess 22 of the semiconductor substrate 20 is deeply shaved off, and the thin diaphragm 21 is formed. This third etching process is performed by forming the insulating films 26, 27 and 30 and connecting electrodes described below.
32, wire bonding pads 31, 35, etc. are formed.

After the first and second etching processes described above, the first insulating film 26 is formed from the step portion 24 of the silicon semiconductor substrate 20 to the wiring groove region 23a (FIG. 7). The first insulating film 26 has a depth of the wiring groove region 23a (a distance between the bottom surface of the wiring groove region 23a and the fixed substrate 10) in order to press-bond the interconnection pads 12a and 32a which will be described later. It is for adjusting. The first insulating film 26 is formed by chemical vapor deposition (CVD).
It is formed by depositing a silicon oxide film (SiO ₂ ) by the n) method.

A second insulating film 27 is formed over the entire upper surface of the first insulating film 26 and the wiring groove 23 (FIG. 8). The second insulating film 27 is also formed by depositing a silicon oxide film (SiO ₂ ).

The step 25 in the wiring groove 23 is filled with the second insulating film 27, and the bottom surface of the groove 23 is smooth. This prevents the electric field from concentrating on the corners of the step 25 when the semiconductor substrate 20 and the fixed substrate 10 are anodically bonded to each other, resulting in a protrusion on the surface of the silicon semiconductor substrate 20 or a connection electrode 12, which will be described later. It is prevented that the wire 32 is broken or the fixed electrode 11 is broken.

Further, the second insulating film 27 is formed in the shallow portion 23b of the wiring groove 23, so that the second insulating film 27 is formed on the bottom surface (surface of the insulating film 27) in the wiring groove 23 and the fixed substrate 10. The groove constriction portion 28 is formed so as to be particularly narrow between the connection electrode 12 and the connection electrode 12 to be formed. Due to the presence of the groove narrowing portion 28, it is possible to prevent dicing dust or dust having a size that affects the sensor characteristics from entering the recess 22. Needless to say, the atmosphere is introduced into the recess 22 (sensor gap) in the sensor through the wiring groove 23.

The groove narrowing portion 28 may be formed so narrow that the connection electrode 12 contacts the second insulating film 27. By forming an insulating film on the inner surface of the region 23b of the wiring groove 23, the lateral width of the groove narrowing portion 28 may be narrowed.

Further, a third insulating film 30 is formed on the side surface portion 29 of the silicon semiconductor substrate 20 exposed on the step portion 24 side (FIG. 9). Although the third insulating film 30 slightly protrudes from the bonding surface of the silicon semiconductor substrate 20 with the fixed substrate 10, the third insulating film 30 is not wide and thick enough to adversely affect the anodic bonding of both substrates 10 and 20. The third insulating film 30 is formed by forming a thermal oxide film on the entire upper surface of the silicon semiconductor substrate 20 (excluding the first and second insulating films 26 and 27), and forming a thermal oxide film on portions other than the portion 29. Are removed by etching. The third insulating film 30 prevents a leak current from flowing from the portion 29 of the semiconductor substrate 20 to the wire bonding pad 31 (described later) and reduces malfunctions.

Thermal oxide film formed on the inner surface of the wiring groove 23
You may leave 30a. The presence of the thermal oxide film 30a prevents the connection electrodes 12 and 32 from coming into contact with the inner surface of the wiring groove 23. Further, an insulating film may be left on the inner peripheral surface of the recess 22.

A hole is formed in the first insulating film 26 and the second insulating film 27 at one end of the upper surface of the step portion 24 of the semiconductor substrate 20. Wire bonding pad for movable electrode in this hole
35 is formed. The wire bonding pad 35 is electrically connected to the movable electrode (diaphragm) 21 through the semiconductor substrate 20.

Further, a fixed electrode wire bonding pad 31 is formed on the other end of the step portion 24 on the second insulating film 27. An elongated connection electrode 32 is formed extending from the fixed electrode wire bonding pad 31 to the middle of the wiring groove 23. An interconnection pad 32a is formed at the tip of the connection electrode 32.

These wire bonding pads 35,
The connection electrode 32 and the connection electrode 32 are formed by sputtering a metal thin film such as aluminum.

A circular fixed electrode 11 which is slightly smaller than the area of the recess 22 is formed at a position facing the recess 22 on the lower surface of the fixed substrate 10. The fixed electrode 11 is formed, for example, by depositing chromium on the fixed substrate 10.

On the lower surface of the fixed substrate 10, elongated connection electrodes 12 are further formed while bending along the wiring grooves 23. The tip of the connection electrode 12 ends in a wiring groove region 23a (a position closer to the step portion 24 than the groove narrowing portion 28), and an interconnection pad 12a is formed at the tip thereof. The connection electrode 12 is formed by depositing gold, for example.

The fixed substrate 10 and the semiconductor substrate 20 are anodically bonded. After the fixed substrate wafer having many sensor parts and the semiconductor substrate are anodically bonded, the wafer is divided into individual sensor chips by dicing. At this time,
The portion of the fixed substrate 10 located above the stepped portion 24 of the semiconductor substrate 20 is also cut off by dicing. Connection electrode 12 and
32 is a groove for wiring 23
The width is slightly narrower than that. When the fixed substrate 10 and the silicon semiconductor substrate 20 are anodically bonded, the interconnection electrodes 12a, 32a of these connection electrodes 12, 32 are connected.
Is crimped vertically. As a result, the fixed electrode 11 and the fixed electrode wire bonding pad 31 are electrically connected.

The fixed electrode 11 and the movable electrode 21 pass through wires (not shown) bonded on the wire bonding pads 31 and 35, respectively, and are connected to an external capacitance measuring circuit (pressure detecting circuit; not shown). Connected.

The pressure to be measured is applied to the diaphragm (movable electrode) 21 from the lower surface of the semiconductor substrate 20 as described above.
The diaphragm (movable electrode) 21 is vertically displaced (vibrated) according to the difference between the atmospheric pressure in the recess 22 and the pressure to be measured. As the gap between the movable electrode 21 and the fixed electrode 11 changes, the capacitance C between these electrodes 21, 11 changes. The change in the capacitance C or the reciprocal 1 / C of the capacitance C (generally, the reciprocal 1 / C is used as a sensor output) is converted into a signal representing pressure by the capacitance measuring circuit. .

The present invention can be applied not only to the capacitance type pressure sensor but also to other capacitance type sensors, for example, the capacitance type acceleration sensor.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a capacitance type pressure sensor.

FIG. 2 is a partially cutaway enlarged plan view of the capacitance type pressure sensor.

FIG. 3 is a sectional view taken along line III-III in FIG. 2;

FIG. 4 is a sectional view taken along line IV-IV in FIG. 2;

5 is a sectional view taken along line VV of FIG.

FIG. 6 is an enlarged perspective view showing a state where a silicon semiconductor substrate is etched.

FIG. 7 is an enlarged perspective view showing a state in which a first insulating film is formed on a silicon semiconductor substrate.

FIG. 8 is an enlarged perspective view showing a state in which a second insulating film is formed on a silicon semiconductor substrate.

FIG. 9 is an enlarged perspective view showing a state in which a third insulating film is formed on a silicon semiconductor substrate.

FIG. 10 is a partially cutaway plan view of a conventional electrostatic capacity type semiconductor pressure sensor.

FIG. 11 is a sectional view taken along line XI-XI in FIG. 10;

12 is a sectional view taken along line XII-XII in FIG.

[Explanation of symbols]

 10 Fixed substrate 11 Fixed electrode 12, 32 Connection electrode 12a, 32a Interconnection pad 20 Silicon semiconductor substrate 21 Diaphragm 23 Wiring groove 26 First insulator 27 Second insulator 28 Groove constriction 30, 30a Third insulation Body 31, 35 Wire bonding pad

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication point H01L 29/84 (72) Inventor Takuya Nakajima 10 Hanazono Todocho, Ukyo-ku, Kyoto-shi, Kyoto Omron shares In the company

Claims (9)

[Claims] 1. A semiconductor substrate and a fixed substrate are bonded to each other, a detection gap is formed between the semiconductor substrate and the fixed substrate, and a part of the semiconductor substrate serves as a movable electrode in the detection gap. A fixed electrode is formed on the fixed substrate at a position facing the movable electrode, and a fixed electrode pad is formed on one of the semiconductor substrate and the fixed substrate, and at least one of the semiconductor substrate and the fixed substrate is formed. On the other hand, a wiring groove is formed from the detection gap toward the fixed electrode pad, and a gap is formed between the wiring groove and the groove wall to fix the fixed electrode to the fixed electrode. A capacitance type sensor in which a connection electrode for connecting to a pad is provided and a constriction structure is formed in a part of the wiring groove. 2. The capacitance type sensor according to claim 1, wherein the wiring groove is smoothly bent substantially at a right angle. 3. The capacitance type sensor according to claim 1, wherein the narrowed structure is formed by providing an insulating film on an inner surface of the wiring groove. 4. A semiconductor substrate and a fixed substrate are bonded to each other, a detection gap is formed between the semiconductor substrate and the fixed substrate, and a part of the semiconductor substrate serves as a movable electrode in the detection gap. A fixed electrode is formed on the fixed substrate at a position facing the movable electrode, and a fixed electrode pad is formed on one of the semiconductor substrate and the fixed substrate, and at least one of the semiconductor substrate and the fixed substrate is formed. On the other hand, a wiring groove is formed from the detection gap toward the fixed electrode pad, and a gap is formed between the wiring groove and the groove wall to fix the fixed electrode to the fixed electrode. A capacitance type sensor in which a connection electrode for connecting to a pad is provided and the wiring groove is smoothly bent at a right angle. 5. The capacitance type sensor according to claim 1, wherein the wiring groove is formed on the semiconductor substrate, and a wiring film is formed on a bottom surface of the wiring groove. 6. The static electrode according to claim 5, wherein the wiring groove has at least two portions having different depths, and the insulating film smoothly connects the boundaries of the portions having different depths. Capacitive sensor. 7. The semiconductor substrate has a portion projecting from a joint portion with the fixed substrate, and the projecting portion is a step portion formed thinner than the joint portion of the fixed substrate, and the semiconductor substrate seen in the step portion. 5. The capacitance type sensor according to claim 1, wherein the cut surface of is exposed, and an insulating film is formed on the exposed cut surface. 8. The connection electrode comprises a first connection electrode extending from a part of the fixed electrode in the wiring groove toward the wire bonding pad, and from the wire bonding pad to the wiring. 5. A second connection electrode extending through the groove in the direction of the fixed electrode, wherein the first connection electrode and the second connection electrode are in contact with each other in the wiring groove. Capacitive sensor according to. 9. The semiconductor substrate and the fixed substrate are bonded to each other, a detection gap is formed between the semiconductor substrate and the fixed substrate, and a part of the semiconductor substrate is movable in the detection gap. The fixed electrode is formed on the fixed substrate at a position facing the movable electrode, and the surface of the portion of the semiconductor substrate exposed to the outside is covered with an insulating film. A known capacitive sensor.